Borrowed a digital camera last night and took a few shots. Here's my engine house made from a Cheerios box with a photocopy of elevation drawings pasted on the side.
I got the drawings from HO Trackside Structures You Can Build (Kalmbach). Many of the older Model Railroader magazines have scale elevation drawings, and permission to photocopy is even granted to the owner of the magazine, so it's all legal!
In this case, I hope to build this engine house eventually. In other cases, I have just put up a mock-up to fill in the space and give me an idea of what it'll look like when done (whenever that will be...).
Gary - just be aware that if you do too good a job on the "mock-up", it might become permanent...!
Andrew, you made a great job of that, why would you want to make another one with that one looking so good? A splash of brick colour and it would look just perfect!